1. Field of the Disclosure
The present disclosure relates to improvements in apparatus for microscopic detection of hardness and related apparatus.
2. Description of the Prior Art
In the prior art, hardness, the resistance of a material to permanent deformation, is typically measured on a Brinell, Rockwell or Vickers hardness testing machine. In a Vickers test, a four-sided pyramidal diamond indenter is pressed into the surface of the test sample with a controlled force. The indenter or the microscope is moved so the indent can be viewed and the lengths of the two diagonals of the indentation in the surface of the test sample are measured. The Vickers hardness of the test sample is calculated, typically by software, using the test force and the area of indentation. In Vickers testing, the indenter is typically a symmetrical four-sided pyramid which produces a square-shaped indentation. In Knoop testing, similar testing equipment is used, but a highly asymmetrical indenter is used, wherein the resulting indent is highly elongated (typically with 7:1 ratio of length to width) and the calculation of hardness is performed based on the measurement of the long diagonal.
Vickers testers may be equipped with multiple indenters (which may include both Vickers and Knoop indenters) and multiple microscope objectives all mounted on a multiple position rotatable turret. The user rotates the turret so as to position the selected indenter above the test sample, the indentation is made and the user rotates the turret so as to position a microscope objective so that the user can view and measure the indentation.
To make symmetrical indentations on a test sample, the diamond indenter must contact the surface with a precise angular orientation. Typically, the indenter axis and the surface of the test sample must be perpendicular in both axes within three arc minutes. Two adjustable horizontal axes are required because such a tight angular tolerance is typically not achievable with fixed parts, even with the most precise machining.
Wilson Tukon 2100 and Tukon 2500 testers use an arrangement of thin shims (0.001″ & 0.003″ thick sheet metal washers) to adjust the angle of the XY stage. Two Knoop indents (one horizontal and one vertical) are made with the unshimmed tester, indent asymmetry is measured and the measurements are used to calculate the thicknesses of the shims needed to correct the asymmetry. The shims are placed around the four bolts that clamp the XY stage to the loadframe. Finally, two more Knoop indents are made to verify the results of shimming. The Wilson Tukon testers use a coarse, uncontrolled stage rotation adjustment.
Moreover, a third indent orientation, rotation of the indent about the viewing axis must also be controlled. Opposite indent corners need to be oriented left-to-right and front-to-back within approximately a half degree. This third indent orientation is generally utilized, because indent length is measured automatically by two pairs of software filars (one pair is exactly vertical and one pair is exactly horizontal), and many users would assume that an indent with a visually perceptible tip angle would be inaccurately measured by the software filars—even though an indent with a very obvious 2.5 degree angle would actually be measured accurately (within 0.1 percent) by the filars.
Manufacturers which may adjust their indenter symmetry include Emco. Co., Qness Co., Futuretec, Newage, and Mitutoyo, possibly among others.
A fourth orientation, the rotation of the stage about the viewing axis must also be tightly controlled. As the stage traverses from left to right or front to back, any sample point must travel exactly horizontally or vertically respectively along the monitor screen.
Occasionally, the XY stage must be removed and/or reassembled to the tester frame (e.g.; when the tester is received by the customer and when servicing the tester). With the prior art stage attachment, the heavy stage must be lifted straight up off the large coarse attachment thread. It is not uncommon for the stage, as it is lifted up for removal from the tester to catch on a holding stud, causing the user to lift the stage with a jerk into the indenter above.
Additionally, a four-axis alignment device, having two translations and two rotations, exists for adjusting the alignment of tensile test specimens. This device is manufactured to the Interlaken Company and may be related to U.S. Pat. No. 5,377,549 entitled “Alignment Device and Method of Aligning”, issued on Jan. 3, 1995 to Werner.
Prior art Vickers testers typically use a motorized turret to position microscope objectives and indenters. However, prior art microscopes often involve moving parts, e.g., bearings and position detent mechanisms. Sometimes, the prior art detent mechanism flexure was prone to fracture and the detent ball could wear a deep groove in the brass track, causing the detent-feel to be lost.
Wilson Tukon 2100 and Tukon 2500 testers use a five-position rotating turret that can hold any combination of microscope objectives and loadcell/indenter assemblies. One position is fixed (“home” position) and the other four positions can be made parcentric to the home position with a series of adjusting bolts.
Emco Co., Qness Co. Futuretec, Newage, and Mitutoyo among others are believed to use a rotating turret to hold and position the objectives and indenters.